In multiple station machines referred to sometimes as automation equipment, each station is designed to perform a certain metal removal function. If an engine block is being carried from station to station, it will have some holes drilled at one station, others at another station, some reaming operations at still another station and probably some face milling operations, and so forth. Each metal removing tool must be advanced to the work and then retracted to allow the work to be moved from one station to another. The timing of each operation is important since seconds saved at any one station will accumulate to hours because of the high production figures in many industries.
In this field of multiple station automatic transfer machines used for metal cutting such as milling, drilling, reaming, or tapping, it is common practice to use, in the stations where such operations are performed, systems referred to as slide or way units on which the tool carriages are mounted and are rapidly advanced towards the workpiece, until the tools almost but not quite touch the workpiece, and then shift to a much lower speed to feed the tools into the workpiece for their respective cutting operations.
In conventional mechanically actuated slide or way units, operated through a lead screw or its equivalent, the transition from rapid advance, high speed motion to relatively slow feed motion is accomplished through some type of friction clutch or brake, engaged at high relative speed. This creates a certain range of uncertainty of the exact position from which the tools advance towards the workpiece at feed speed. The same is true if hydraulic feed and retract units are used since exact control is difficult.
It is one object of this invention to provide a system in which the slide or carriage carrying the tools is rapidly advanced towards the workpiece using a predetermined accelerated-decelerated motion, as opposed to the conventional substantially constant speed rapid advance motion which is abruptly decelerated to feed speed.
It is another object of this invention to provide a system in which the transition from rapid advance motion to feed motion is a very exact and reproducible position of the slide or carriage on which the tools are mounted. This not only provides a saving of time but also insures that no tool breakage will occur.
At the end of the feed movement or stroke, it is conventional practice for the tool carriage to be returned to its original starting position through a relatively high speed rapid return stroke. This is generally accomplished by the same constant speed drive mechanism used for the rapid advance stroke and results in very large short acceleration at the beginning of the rapid return stroke and a very high short deceleration at the end of this same stroke.
It is, therefore, another object of this invention to provide a system in which the slide or carriage carrying the tools is rapidly returned to its starting position using an accelerated-decelerated motion having a stroke which is the sum of the previous rapid advance motion and feed motion.
Other objects and features of this invention will be apparent in the following description and claims in which the principles of the invention are set forth together with details directed to those skilled in the art to enable them to practice the invention, all in connection with the best mode presently contemplated.